Mixing or stirring apparatus



April 19, 1955 STAAF 2,706,622.

I MIXING OR STIRRING APPARATUS Filed Nov. 25, 1952 3 Sheets-Sheet 1 II I! April 19, 1955 G. A. STAAF MIXING OR STIRRING APPARATUS 3 Sheets-Sheet 2 Filed Nov. 25, 1952 .llililil Ilill Fig. 3

G Ac A avey April 19, 1955 G. A. STAAF MIXING 0R STIRRING APPARATUS 3 Sheets-Sheet 3 Fig. 5

Filed Nov. 25, 1952 United States Patent MIXING 0R STIRRING APPARATUS Gustaf Adolf Staaf, Vasteras, Sweden Application November 25, 1952, Serial No. 322,384

9 Claims. (Cl. 259-96) This invention relates to apparatus for mixing or stirring together liquids or a mixture of liquids and solids or semi-solids. Mixing or stirring apparatus of said kind are widely used for rapidly mixing different liquids, to ac celerate the mixing of layers of liquid of different temperature, to accelerate a chemical reaction between a solid and a liquid or between two liquids, to accelerate the dissolving of a solid in a liquid or of a liquid in another liquid, to keep solid particles in suspension in a liquid, and for other similar purposes.

In mechanical mixing apparatus there is usually used as stirring member a spider which is brought to rotate in the vessel containing the liquid, or one or more propellers, which rotate in the liquid. Mixing apparatus provided with rotatable spiders as a rule require, however, heavy shafts and shaft bearings, usually with one bearing placed on the bottom of the liquid container, to be able to take up the unbalanced radial forces set up by the stirring member, this being a considerable inconvenience particularly in such cases where solid particles are present in the liquid or the liquid has no lubricating capacity. Mixing apparatus provided with rotatable propellers do not require a bottom bearing, but very great axial forces are set up, which particularly in the case of long propeller shafts require heavy shafts and shaft bearings.

To avoid said inconvenience it has been proposed to use a pump wheel as a stirring member. When using a pump wheel as a stirring member no resulting radial force is set up, wherefore it is usually not necessary to provide a bottom bearing for the shaft, and the axial forces are small and can be brought to entirely neutralize each other by using a pump wheel designed to suck in the liquid in an axial direction from both sides.

Mixing apparatus comprising a stirring member in the form of a pump wheel have, however, similarly to other known mechanical mixers provided with a rotatable stirring member, the inconvenience that the stirring member has a tendency of putting the entire body of liquid in the container in a rotating motion, which in certain cases can reach a number of revolutions which is only slightly smaller than the number of revolutions of the stirring or mixing member. Said phenomenon greatly reduces the stirring effect, since the latter is dependent on the difference in number of revolutions between the stirring member and the liquid. If the liquid rotates rapidly, there is furthermore formed in the liquid a crater through which air is sucked into the liquid, which in many cases is not permissible. In such cases, when the stirring is effected to keep solid particles suspended in a liquid, the rotation of the liquid involves the particular inconvenience that the suspended particles, on account of the centrifugal force, will be concentrated to the sides of the container.

The present invention has for its object to eliminate, in mechanical mixing or stirring apparatus having a stirring member in the form of a pump wheel which is rotatable about a vertical axis, the tendency of the stirring member to set the entire body of liquid in the liquid container in rotation. According to the invention, said object has been obtained by enclosing the pump wheel in a pump housing, which on the pressure side of the pump wheel has a liquid outflow passage, and by arranging in said passage a number of substantially radially and vertically positioned guide plates, which serve to brake the rotational movement in which the liquid is set by the pump wheel during its passage through the latter.

The invention will now be described more in detail ice with reference to the accompanying drawings, in which:

Figure 1 shows a first embodiment of the invention.

Figure 2 is an axial section on a larger scale through the pump wheel, and pump housing of Figure 1.

Figure 3 is a section on the line 3-3 in Figure 2.

gigure 4 is a bottom view corresponding to Figure 2, an

Figure 5 shows a second embodiment.

In Figure l, the reference numeral 10 designates a liquid container, on the upper edge of which are placed two beams 11, which support an electric driving motor 12 having a vertical shaft. Coupled with the shaft of the driving motor is a vertical extension shaft 13 which at its lower end carries a pump wheel 14 having a central suction opening on its underside. Threaded over the pump wheel shaft 13 is a tube 15, which is suspended in the beams 11 and reaches almost down to the upper side of the pump wheel 14. The pump wheel 14 is enclosed in a housing in the form of a cylinder 16, which is coaxial with the pump wheel and is open at its upper end, said cylinder being suspended in the tube 15 through the intermediary of a plurality of vertically and radially directed guide plates 17. At its lower end the pump housing cylinder 16 reaches with radially drawn-in deflecting surfaces 18 almost onto the pump wheel 14.

As shown more clearly in Figures '2 to 4, the pump wheel 14 has six radially directed vanes 9. The pump wheel is designed for the passage of a comparatively great amount of liquid at low speed without considerable pressure rise, the axial dimension of the annular outflow opening being, for instance, one tenth of the diameter of the pump wheel. The central suction opening of the pump wheel has the same area as the annular outflow opening, the flow passage area being generally constant throughout the pump wheel.

The clearance or play between the pump wheel 14 and the adjacent edge of the pump wheel housing 16, 18 is sufficient to permit the pump wheel to oscillate laterally with an amplitude, which is of the order of magnitude of one tenth of the diameter of the pump wheel. Such oscillations may be set up during starting and stopping of the driving motor in case the critical speed of the motor shaft and the shaft extension 13 is lower than the operating speed of the motor, particularly in case the motor has to be started slowly.

In the embodiment illustrated in Figures 2 to 4 sixteen axially and radially directed guide plates 17 have been provided in the pump housing cylinder 16. The area of the outflow opening of the pump housing is equal to or larger than the area of the outflow opening of the pump wheel. The maximum distance between two adjacent guide plates 17 has been selected smaller than the dimension of the guide plates in the direction of flow.

The mixing or stirring apparatus described operates in the following manner. When the driving motor 12 puts the pump wheel 14 in rotation, liquid is sucked in through the downwardly directed central opening of the pump wheel, is pressed by the vanes of the pump wheel radially out into the pump housing 16, and flows through said housing along the deflecting surfaces 18 and thereafter in an axial direction upwards and out through the annular passage formed between the wall of the pump housing cylinder 16 and the supporting tube 15, the rotation in which the liquid has been set by the pump wheel during its passage through the latter being braked by the guide plates 17 arranged in the outflow passage transversely to the direction of rotation. From the outflow passage the liquid rises substantially vertically, bends gradually off in a radial direction towards the sides of the container, and thereafter flows downwardly substantially in parallel with the sides and along the bottom of the container to the center of the latter, where the liquid is again sucked into the pump wheel, whereafter the cycle is repeated. The liquid currents produced by the mixer in the container 10 are indicated in the drawing figure with a number of arrows. In order that the amount of liquid contained in the supporting tube 15 shall take part in the flow the supporting tube is preferably provided with perforations.

It should be particularly noted that the guide plates 17 arranged in the annular outflow passage from the pump housing 16 only serve to prevent the entire body of liquid of the container from rotating, whereas an even flow of liquid past the guide plates is not desired. Because of the fact that in the embodiment shown the guide members consist of radially positioned plane plates and thus are not properly shaped from a hydrodynamic point of view, there are produced in the liquid during its passage past the guide members whirls or eddy currents, which have an advantageous effect in that they intensify and accelerate the stirring or mixing.

The embodiment according to Figure 5 differs from the one shown in Figures 1 to 4 in the first instance thereby, that the pump whcel 14 is turned with its central suction opening upwards and that the pump housing is turned around. Furthermore, the supporting tube 15 for the guide members 17 and the pump housing 13 is arranged standing on the bottom of the container 10. Through the downwardly directed outflow passage, which contains the guide plates 17, the liquid flows in an axial direction downwards towards the bottom of the vessel 10 and along the bottom towards the sides thereof, along said sides and radially inwardly back to the suction opening of the pump wheel 14. In order to make the flow in upper layers of liquid in the container more lively, the cylindrical pump housing 16 is provided with an upwardly directed extension 19.

In the embodiment shown in Figure 5, in which the liquid is sucked into the pump wheel from above and is pressed out of the pump housing downwardly towards the bottom of the liquid container, is particularly suitable in cases when it is desired to keep the particles in a liquid suspension suspended in the liquid, or when it is desired 0t dissolve solid particles in a liquid.

The forces which in the different embodiments act on the pump wheel are, as already mentioned, on the one hand radially directed and on the other hand axially or vertically directed. The radial forces neutralize each other, wherefore no resulting radially directed force is at hand, wherefore it is not necessary to support the pump wheel shaft in a bearing at its lower end. By suitably shaping the pump wheel the axial forces can be kept so low that, as a rule, the pump wheel shaft can be coupled directly to the shaft of the driving motor 12 and the bearings of the driving motor alone provide the bearings for the entire rotating system. Therefore the mixer can advantageously be made as a unit, which can be moved between different containers, whereby the number of necessary mixers for a certain plant can be kept down.

It should be particularly noted that in all the embodiments disclosed there is a considerable play between the pump wheel and the pump housing, this being generally a necessary condition for the elimination of a lower bearing for the pump wheel shaft.

The invention is, of course, not limited to the embodiments shown on the drawing and described in detail above, but modifications of different kinds are conceivable within the area of the invention.

I claim:

1. An apparatus for mixing liquids comprising an elongated free-hanging rotatable shaft member adapted to be mounted within a container, a stirring member mounted at the lower end of said shaft member and comprising an impeller of the centrifugal pump type, a housing adjacent said impeller for controlling the flow of the liquid agitated by the said impeller, said housing having an annular outlet opening disposed substantially coaxial with the rotational axis of said impeller, the flow passage area of said opening being larger than the flow passage area of said impeller, said housing comprising a substantially hollow cylindrical member disposed substantially coaxial with said impeller, said cylindrical member being open at one end to effect said annular outflow opening adjacent one end of said impeller, the other end of said cylindrical member also being open and being arcuately drawn in toward said impeller to define curved inflow deflecting surfaces for said housing adjacent the said impeller, said impeller being so mounted on said shaft member with respect to said housing that considerable lateral oscillation of said impeller with respect to said housing is permitted, and a plurality of substantially vertical guide plates radially disposed with respect to said impeller, said guide plates being mounted in said housing in said outflow opening.

2. The apparatus of claim 1 wherein said annular outflow opening is disposed upwardly with respect to said impeller. I

3. The apparatus of claim 1 wherein said annular outflow opening is disposed downwardly with respect to said impeller.

4. An apparatus for mixing liquids comprising a container, an elongated vertically mounted rotatable shaft member within said container, a stirrnig member coupled to said shaft member and comprising an impeller of the centrifugal pump type, a housing adjacent said impeller for controlling the flow of the liquid agitated by the said impeller, said housing comprising a substantially hollow cylindrical member disposed substantially coaxial with said impeller, a supporting tube inserted into and substantially coaxial with said cylindrical member for carrying said cylindrical member, said cylindrical member being open at one end to define an annular outflow opening disposed substantially parallel to the rotational axis of said impeller between said cylindrical member and said supporting tubes, the flow passage area of said outflow opening being larger than the flow passage area of said impeller, the other end of said cylindrical member also being open and being radially drawn in toward said impeller to define inflow deflecting surfaces adjacent the said impeller, and a plurality of substantially vertical guide plates radially disposed with respect to said impeller between said cylindrical member and said supporting tube adjacent said outflow opening, said impeller being so mounted on said shaft member with respect to said housing that considerable lateral oscillation of said impeller, with respect to said housing, is permitted.

5. The apparatus of claim 4 wherein said supporting tube is mounted at one of its ends on the bottom of said container.

6. The apparatus of claim 4 including a frame structure mounted between said container and said supporting tube, and a driving motor coupled to said shaft member and supported by said frame structure.

7. An apparatus for mixing liquids comprising an elongated shaft member mounted free-hanging for rotation in a container, a stirring member positively coupled to said shaft member, said stirring member comprising an impeller, having a plurality of radially disposed vanes, of the centrifugal pump type, and a housing member substantially surrounding said impeller and including supporting means, said housing comprising a substantially cylindrical member hollow in configuration and open at one of its ends adjacent said impeller to effect an outflow opening, said housing being drawn in toward said impeller at the other of its ends thereby to provide an inflow opening and liquid deflection surfaces adjacent thereto, said supporting means including a tube-like member inserted into and coaxial with said cylindrical housing, said outflow opening being defined between the periphery of said housing and the surface of said tube-like member whereby said outflow opening is substantially annular in configuration, said impeller being so supported adjacent said inflow opening that substantial lateral motion of said shaft member and impeller with respect to said housing is permitted, and a plurality of guide plates within said housing and adjacent said outflow opening, said guide plates being substantially vertical and being disposed radially with respect to said impeller.

8. The apparatus of claim 7 in which said tube-like member is substantially coextensive with and surrounds said elongated shaft member, and motor driving means mounted adjacent said container and coupled to one end of said shaft member.

9. An apparatus for mixing liquids comprising a container, a free-hanging elongated shaft disposed within said container, driving means adjacent said container and coupled to one end of said shaft for rotating said shaft, an impeller unit positively coupled to said shaft for rotation therewith, said impeller unit including a pump wheel hav ing a plurality of radially disposed vanes, a substantially cylindrical housing surrounding said impeller unit and substantially coaxial therewith and having supporting means coupled to said container, said housing defining an outflow opening. at one of its ends, through which liquid may be pumped in a direction substantially parallel to that of said elongated shaft, a plurality of planar guide plates within said housing adjacent said outflow opening and radially disposed with respect to said impeller unit, said supporting means including an elongated tube-like member mounted at one of its ends on said container and having its other end inserted into said housing and substantially coaxial therewith, said guide plates being mounted between the said housing and the inserted portion of the said tube-like member, said housing being directed inwardly, at the other of its ends, toward said pump wheel thereby to provide integral liquid deflection means adjacent said pump wheel. 5

References Cited in the file of this patent UNITED STATES PATENTS 59,282 Shannon Oct. 30, 1866 10 6 Smith et a1. Mar. 11, 1890 Groch Oct. 15, 1918 Beers June 10, 1930 Duwe Dec. 23, 1930 Allen et a1 June 2, 1936 Daman et al May 27, 1941 Kurz Feb. 1, 1949 

